The present invention was conceived as a repair to a bouncy floor problem in the inventor""s home. The dining room of the inventor""s home is supported by typical framed construction with nominal 2 inchxc3x9710 inch Douglas Fir floor joists spaced 16 inches on center to carry the floor load. One of the floor joists was noticeably weaker than the others due to large knots and grain flaws and allowed an undesirable amount of deflection in that area of the floor when stepped on.
The deflection was removed by attaching a perforated steel strap to the underside of the weak joist at each end and tensioning said strap with opposed wedges at the center of the span. The strap and wedge combination provided additional tensile strength to the bottom chord of the weak joist as well as support to the center span area where the wedges pressed up against the bottom of said joist. After application of the invention the weak floor joist no longer deflected under normal floor loads, and was in fact more rigid than other joists adjacent to it.
Other beam strengthening devices are illustrated in U.S. Pat. Nos. 2,856,644; 3,427,773; and 5,806,259. It becomes evident from review of the known devices that while they rely on the same principles of physics as the present invention to strengthen the beam, they are substantially more complex, more difficult to install and more expensive to manufacture. Furthermore, none of the prior art utilizes a perforated flat metal strap, which is inherently easy to attach to the beam. Additionally none of the prior art has the simple tensioning devices claimed in the present invention or the flexibility of the present invention, which could be sold in bulk and cut to appropriate lengths on the work site.
The object of the present invention is to provide a simple, low cost means of strengthening spanning structural wood members. The invention has applications in the strengthening of existing spanning members such as inadequate joists or rafters already in place in a structure. The invention could also be used to increase spans or reduce the size of spanning wood members in new construction. Another application might be in a pre-manufactured truss-beam combination. The inventor has been engaged in the construction of wood frame buildings for over 27 years and has seen no prior art that utilizes a tensioned steel strap to strengthen a spanning wood member.
The present invention provides a device for enhancing the load carrying capacity of new or existing, spanning, structural lumber. The device consists of a steel strap, attached at both ends of a spanning structural member by means of standard fasteners such as nails, screws or bolts and running parallel to the long axis of the member either on the bottom or along the side. The strap is then tensioned by means of a central expanding device such as opposed wedges, or a screw device. The tensioning of the strap has the effect of adding tensile strength to the bottom chord of the spanning structural member as well as supporting the center of the member.